Light olefins are an important basic chemical feedstock for the production of many plastics used in a variety of industries. Olefins are most commonly produced from petroleum feedstocks through the cracking of larger hydrocarbon molecules. The cracking process is either a catalytic or steam cracking process, and produces light olefins which consist primarily of ethylene and propylene.
An alternate source of light olefins is from the conversion of oxygenates to olefins. The primary oxygenate that is converted to an olefin is methanol. The preferred process is generally referred to as methanol-to-olefins (MTO) process. The primary olefins produced from this process are ethylene and propylene, and the process is performed over a catalytic molecular sieve. The MTO process enables an important alternative to petroleum sources of feeds for the production of light olefins. The sources of oxygenates include alcohols, such as methanol and ethanol; ethers, such as dimethyl ether and diethyl ether; and other oxygenates, such as methyl formate and dimethyl carbonate. These oxygenates can be produced from natural gas, fermentation of biomass, municipal wastes, and recycled organic materials. An important commercial consideration is that methanol can be readily produced from natural gas, or coal, and is easier and safer to handle and transport then either natural gas or coal.
There are numerous patents describing improved preparation of zeolites. U.S. Pat. No. 3,957,689 describes a process for making attrition resistant faujasite zeolites. U.S. Pat. No. 4,987,110 describes a process for making attrition resistant molecular sieves by adding a clay and aluminum chlorhydroxide. U.S. Pat. No. 5,352,645 describes a process for producing hardened silica microspheres. U.S. Pat. No. 6,362,128 describes a process for producing catalysts having oxide-rich outer layers with improved attrition resistance. U.S. Pat. No. 6,589,902 describes a process for producing attrition resistant materials containing crystalline anionic clays and U.S. Pat. No. 6,878,668 describes a process for producing attrition resistant vanadium/phosphorous oxide catalyst. In view of the above prior art, it can be seen that the type of molecular sieve or catalyst, composition, size, and processing conditions affect the process of producing attrition resistant particles, and requires significant experimentation without providing guidance for specific molecular sieves.
The environment for the production of methanol to olefins, i.e. the reactor, is a severe physical environment. The reactor is generally a fluidized bed, and the catalyst particles are subject to constant rubbing against other particles and the reactor walls, as well as physical contact with other equipment. This tends to break down the catalyst particles, causing fines which need to be removed from the system, as well as shortening the life of the catalyst particles. It would be useful to produce a catalyst that is more attrition resistant, and therefore has a longer, more economical life.